In building construction, there is a light-weight steel frame ceiling made by suspending hanging bolts from a ceiling slab, using the hanging bolt to assemble ceiling bars and ceiling bar supports into a lattice, and suspending boards on the lattice. The ceiling bars and ceiling bar supports used in this ceiling are defined by JIS in the classification of steel furrings for wall and ceiling in buildings. The steel furrings are plate-shaped steel having a thickness of 0.5 mm that is formed by bending into a U shape. Hereinafter, the steel furrings will be referred to as an angle iron.
Conventionally, angle irons are cut to match the length of boards using a power grinder, for example. Because the grinder is power driven, the angle iron can be cut in just a few seconds. However, grinding dust and chips may be scattered around ambient objects and sparks may fly around due to high speed rotation of the grinding stone.
A hand-driven tool for overcoming this problem is disclosed in Japanese Patent-Application Publication HEI-9-108931. The hand-driven tool includes a reception plate and a movable blade. The reception plate is for supporting the angle iron and matches the shape of the angle iron to be cut. The movable blade is disposed in confrontation with the reception plate. The movable blade has thin and sharp blade tip, and is capable of reciprocal movement. By manually operating a lever several times, the movable blade moves toward the reception plate, so that the angle iron that is supported by the reception plate is pressingly cut by shearing force. Because the angle irons are pressingly cut by the movable blade, this device has the merit of not generating cutting dust. On the other hand, there are problems in that the user's hand can become tired because the device is manually operated and also cutting takes a long time to complete.
It is conceivable to make the device into a power tool for eliminating the problem of the user's hand getting tired and for reducing cutting time. However, making the device into an electric power tool involves the following problems.
First, a large space is required for setting the angle iron between the reception plate and the movable blade. Because the movable blade must be moved by the distance of the space, the time required for cutting is increased and safety measures must be considered to prevent objects from entering into the space while the angle iron is being cut. Also, although a great cutting force of 600 to 800 Kg is needed, it is extremely difficult to secure such a large cutting force. It is conceivable to use hydraulics but this would made the configuration complex and expensive.
Taking the above-described problems into account, it is an object of the present invention to provide an inexpensive electrically powered reciprocal-movement power tool capable of providing a large cutting force using a simple configuration and without generating cutting dust.